Question

The diagram shows a blood vessel containing red blood cells, next to some muscle cells. Substances are exchanged between the blood vessel and the muscle cells.
Which of the following gives the correct names for substances X and Y?

• A. X- Carbon dioxide, Y- Oxygen
• B. X- Glucose, Y- Carbon dioxide
• C. X- Oxygen; Y- Glucose
• D. X- Glucose, Y- Oxygen

Answer 1

Answer: (A)

X- Carbon dioxide, Y- Oxygen

The change in partial pressure from the alveoli (high concentration) to the capillaries (low concentration) drives the oxygen into the tissue and the carbon dioxide into the blood (high concentration) from the tissues (low concentration), which is then returned to the lungs and exhaled. Once in the blood of the capillaries, the O${}_2$ binds to the hemoglobin in red blood cells which carry it to the tissues where it dissociates to enter the cells of the tissues. The lungs never fully deflate, so air that is inhaled mixes with the residual air left from the previous respiration, resulting in a lower partial pressure of oxygen within the alveoli.

Therefore, the correct answer is option A.